1. Field of the Invention
The present invention relates to a color image forming apparatus and a scanning optical apparatus and, more particularly, to those arranged to record color image information or the like with suppressing scanning line deviation among colors and with suppressing asymmetric magnification (component of slope of magnification) (image height deviation), for example, such as those suitably applicable to such apparatus as laser beam printers, color digital copiers, etc. having the color electrophotographic process.
2. Related Background Art
In the conventional scanning optical apparatus used in the laser beam printers (LBPs), digital copiers, and so on, light emitted from light source means while optically being modulated according to an image signal is deflected periodically by an optical deflector, for example, by a rotary polygon mirror (polygon mirror), and a scanning optical element (imaging element) having the fxcex8 characteristics focuses the deflected light in a spot shape on a surface of a photosensitive recording medium (photosensitive drum) so as to optically scan the surface, thereby carrying out image recording.
FIG. 1 is a schematic diagram to show the main part of a conventional scanning optical apparatus of this type.
In the same figure divergent light emitted from light source means 91 is collimated into a nearly parallel beam by collimator lens 92 and the beam (amount of light) is limited by stop 93 to enter a cylinder lens (cylindrical lens) 94 having a predetermined refractive power only in the sub-scanning direction. The nearly parallel beam incident to the cylinder lens 94 is emergent in the state of the nearly parallel beam in the main scanning cross section as it is. In the sub-scanning cross section the beam is converged to be focused as an almost line image on a deflection surface (reflective surface) 95a of an optical deflector 95 comprised of the rotary polygon mirror (polygon mirror).
The beam deflected and reflected by the deflection surface 95a of the optical deflector 95 is guided through a scanning optical element (fxcex8 lens) 96 having the fxcex8 characteristics onto a photosensitive drum surface 98 as a surface to be scanned and the photosensitive drum surface 98 is optically scanned with the beam in the direction of arrow F by rotating the optical deflector 95 in the direction of arrow E. This effects image recording on the photosensitive drum surface 98 which is a recording medium.
FIG. 2 is a schematic diagram to show the main part of a color image forming apparatus for forming a color image by simultaneously using a plurality of such scanning optical devices described above to record image information of colors on respective photosensitive drum surfaces different from each other.
In the same figure numerals 111, 112, 113, 114 each denote the scanning optical devices, 131, 132, 133, 134 each the photosensitive drums as image carrying members, 121, 122, 123, 124 each developing units, and 141 a conveying belt. The color image forming apparatus illustrated in FIG. 2 has the four scanning optical devices described above (111, 112, 113, 114), which correspond to the colors C (cyan), M (magenta), Y (yellow), and B (black) respectively, and the apparatus is arranged to record image signals on the respective surfaces of the photosensitive drums 131, 132, 133, 134 in tandem, thereby printing the color image at high speed.
Since the color image forming apparatus of this type forms the image by superposition of plural scanning lines, it is particularly important to reduce the scanning line deviation (which will also be referred to as xe2x80x9cregistration deviationxe2x80x9d) among the colors.
A method for regulating (correcting) this scanning line deviation is, for example, a method for forming registration detection images of the respective colors (cyan, magenta, yellow, and black) on a transfer medium accurately conveyed on the transfer belt, detecting positions of the respective registration detection images by a detecting device, and electrically regulating the deviation, based on the signals thus detected.
There was, however, a problem that it was very difficult to electrically regulate this scanning line deviation and it cost high in terms of the cost.
Further, there was another problem that it was very difficult in the color image forming apparatus of this type to correct the asymmetric magnification (component of slope of magnification) (image height deviation) in the main scanning direction on the surfaces of the image carrying members by simple structure.
An object of the present invention is to provide a compact color image forming apparatus suitable for high-resolution printing, the color image forming apparatus having a plurality of scanning optical devices, wherein slant deviation of a scanning line and curving of a scanning line in each scanning optical device is adjusted by displacing a diffracting optical element of a diffraction section of each scanning optical device whereby the registration deviation in the sub-scanning direction among the colors can be suppressed by the simple structure and wherein the asymmetric magnification (component of slope of magnification) in the main scanning direction on the surface of the image carrying member in each scanning optical device is adjusted by displacing a refraction section or a scanning section comprising the refraction section and a deflecting element or/and the diffraction section in each scanning optical device in the main scanning direction whereby the image height deviation can be suppressed by the simple structure, and also to provide the scanning optical device.
A color image forming apparatus of the present invention is a color image forming apparatus comprising plural sets of a scanning optical device and an image carrying member corresponding thereto, said scanning optical device having an imaging system comprising a refraction section having at least one refracting optical element and a diffraction section having at least one diffracting optical element, the color image forming apparatus being arranged to guide light emitted from each scanning optical device onto a surface of each corresponding image carrying member, to scan the surfaces of the image carrying members with the respective beams, to form images of different colors on the surfaces of the respective image carrying members, and to form a color image from the images formed on the surfaces of the plural image carrying members,
wherein each of the plurality of scanning optical devices is arranged in such a manner that an irradiation position of the light on the surface of the image carrying member is adjusted by displacing the diffracting optical element.
Particularly, the color image forming apparatus is characterized:
in that said diffracting optical element is constructed as a separate unit from the other optical elements forming said scanning optical device;
in that a direction of displacement of the diffracting optical element is a direction of rotation about the optical axis or a direction of rotation about an axis along the longitudinal direction of the diffracting optical element and the diffracting optical element is arranged to be rotatable independently in each of these directions;
in that a slant of a scanning line on the surface of said image carrying member is adjusted by rotating said diffracting optical element about the optical axis or within a plane normal to the optical axis;
in that a curve of a scanning line on the surface of said image carrying member is adjusted by rotating said diffracting optical element about the axis along the longitudinal direction of the diffracting optical element;
in that said diffracting optical element is displaced based on a signal from detecting means for detecting registration;
in that said diffracting optical element has a power in the main scanning direction and a power in the sub-scanning direction, said powers being different from each other;
in that said refraction section has a plastic toric lens having a power in the main scanning direction and a power in the sub-scanning direction, said powers being different from each other; and so on.
Another color image forming apparatus of the present invention is a color image forming apparatus comprising plural sets of a scanning optical device and an image carrying member corresponding thereto, said color image forming apparatus being arranged to guide light emitted from each scanning optical device onto a surface of each corresponding image carrying member, to scan the surfaces of the image carrying members with the respective beams, to form images of different colors on the surfaces of the respective image carrying members, and to form a color image from the images formed on the surfaces of the plural image carrying members,
each of said plural scanning optical devices comprising:
light source means comprising a semiconductor laser;
a first optical element for converting light emitted from the light source means into a substantially parallel beam;
a second optical element for focusing the substantially parallel beam thus converted, into a line image longitudinal in the main scanning direction on a deflection surface of a deflecting element; and
a third optical element comprising a refraction section having at least one refracting optical element and a diffraction section having at least one diffracting optical element for focusing a beam deflected by the deflecting element in a spot shape on the surface of the image carrying member,
wherein each of said plural scanning optical devices is arranged in such a manner that an irradiation position of the beam on the surface of the image carrying member is adjusted by displacing the diffracting optical element.
Particularly, the color image forming apparatus is characterized:
in that said diffracting optical element is constructed as a separate unit from the other optical elements forming said scanning optical device;
in that a direction of displacement of the diffracting optical element is a direction of rotation about the optical axis or a direction of rotation about an axis along the longitudinal direction of the diffracting optical element and the diffracting optical element is arranged to be rotatable independently in each of these directions;
in that a slant of a scanning line on the surface of said image carrying member is adjusted by rotating said diffracting optical element about the optical axis or within a plane normal to the optical axis;
in that a curve of a scanning line on the surface of said image carrying member is adjusted by rotating said diffracting optical element about the axis along the longitudinal direction of the diffracting optical element;
in that said diffracting optical element is displaced based on a signal from detecting means for detecting registration;
in that said diffracting optical element has a power in the main scanning direction and a power in the sub-scanning direction, said powers being different from each other;
in that said refraction section has a plastic toric lens having a power in the main scanning direction and a power in the sub-scanning direction, said powers being different from each other; and so on.
A scanning optical device of the present invention is a scanning optical device for scanning a surface to be scanned, using an imaging system comprising a refraction section having at least one refracting optical element and a diffraction section having at least one diffracting optical element,
said scanning optical device being arranged in such a manner that an irradiation position of a beam on the surface to be scanned is adjusted by displacing the diffracting optical element.
Particularly, the scanning optical device is characterized:
in that said diffracting optical element is constructed as a separate unit from the other optical elements forming said scanning optical device;
in that a direction of displacement of the diffracting optical element is a direction of rotation about the optical axis or a direction of rotation about an axis along the longitudinal direction of the diffracting optical element and the diffracting optical element is arranged to be rotatable independently in each of these directions;
in that a slant of a scanning line on the surface to be scanned is adjusted by rotating said diffracting optical element about the optical axis or within a plane normal to the optical axis;
in that a curve of a scanning line on the surface to be scanned is adjusted by rotating said diffracting optical element about the axis along the longitudinal direction of the diffracting optical element;
in that said diffracting optical element has a power in the main scanning direction and a power in the sub-scanning direction, said powers being different from each other;
in that said refraction section has a plastic toric lens having a power in the main scanning direction and a power in the sub-scanning direction, said powers being different from each other; and so on.
A further color image forming apparatus of the present invention is a color image forming apparatus comprising plural sets of a scanning optical device and an image carrying member corresponding thereto, said scanning optical device having an imaging system comprising a refraction section having at least one refracting optical element and a diffraction section having at least one diffracting optical element, the color image forming apparatus being arranged to guide light emitted from each scanning optical device onto a surface of each corresponding image carrying member, to scan the surfaces of the image carrying members with the respective beams, to form images of different colors on the surfaces of the respective image carrying members, and to form a color image from the images formed on the surfaces of the plural image carrying members,
wherein each of said plural scanning optical devices is arranged in such a manner that asymmetric magnification (component of slope of magnification) in the main scanning direction on the surface of the image carrying member is adjusted by displacing the refraction section or a scanning section comprising the refraction section and a deflecting element or/and the diffraction section in the main scanning direction.
Particularly, the color image forming apparatus is characterized:
in that said diffracting optical element is constructed as a separate unit from the other optical elements forming said scanning optical device;
in that each unit of said refraction section or the scanning section comprising the refraction section and the deflecting element and said diffraction section is fixed to a sheet metal stay;
in that a direction of displacement in the main scanning direction of said refraction section or the scanning section comprising the refraction section and the deflecting element and said diffraction section is a direction parallel to the main scanning direction or a direction of rotation about the optical axis within a plane including the main scanning direction;
in that said diffracting optical element has a power in the main scanning direction and a power in the sub-scanning direction, said powers being different from each other;
in that said refraction section has a plastic toric lens having a power in the main scanning direction and a power in the sub-scanning direction, said powers being different from each other; and so on.
Still another color image forming apparatus of the present invention is a color image forming apparatus comprising plural sets of a scanning optical device and an image carrying member corresponding thereto, said color image forming apparatus being arranged to guide light emitted from each scanning optical device onto a surface of each corresponding image carrying member, to scan the surfaces of the image carrying members with the respective beams, to form images of different colors on the surfaces of the respective image carrying members, and to form a color image from the images formed on the surfaces of the plural image carrying members,
each of said plural scanning optical devices comprising:
light source means comprising a semiconductor laser;
a first optical element for converting light emitted from the light source means into a substantially parallel beam;
a second optical element for focusing the substantially parallel beam thus converted, into a line image longitudinal in the main scanning direction on a deflection surface of a deflecting element; and
a third optical element comprising a refraction section having at least one refracting optical element and a diffraction section having at least one diffracting optical element for focusing a beam deflected by the deflecting element in a spot shape on the surface of the image carrying member,
wherein each of said plural scanning optical devices is arranged in such a manner that asymmetric magnification (component of slope of magnification) in the main scanning direction on the surface of the image carrying member is adjusted by displacing the refraction section or a scanning section comprising the refraction section and the deflecting element or/and the diffraction section in the main scanning direction.
Particularly, the color image forming apparatus is characterized:
in that said diffracting optical element is constructed as a separate unit from the other optical elements forming said scanning optical device;
in that each unit of said refraction section or the scanning section comprising the refraction section and the deflecting element and said diffraction section is fixed to a sheet metal stay;
in that a direction of displacement in the main scanning direction of said refraction section or the scanning section comprising the refraction section and the deflecting element and said diffraction section is a direction parallel to the main scanning direction or a direction of rotation about the optical axis within a plane including the main scanning direction;
in that said diffracting optical element has a power in the main scanning direction and a power in the sub-scanning direction, said powers being different from each other;
in that said refraction section has a plastic toric lens having a power in the main scanning direction and a power in the sub-scanning direction, said powers being different from each other; and so on.
A further scanning optical device of the present invention is a scanning optical device for scanning a surface to be scanned, using an imaging system comprising a refraction section having at least one refracting optical element and a diffraction section having at least one diffracting optical element,
said scanning optical device being arranged in such a manner that asymmetric magnification (component of slope of magnification) in the main scanning direction on the surface to be scanned is adjusted by displacing the refraction section or a scanning section comprising the refraction section and a deflecting element or/and the diffraction section in the main scanning direction.
Particularly, the optical scanning device is characterized:
in that said diffracting optical element is constructed as a separate unit from the other optical elements forming said scanning optical device;
in that each unit of said refraction section or the scanning section comprising the refraction section and the deflecting element and said diffraction section is fixed to a sheet metal stay;
in that a direction of displacement in the main scanning direction of said refraction section or the scanning section comprising the refraction section and the deflecting element and said diffraction section is a direction parallel to the main scanning direction or a direction of rotation about the optical axis within a plane including the main scanning direction;
in that said diffracting optical element has a power in the main scanning direction and a power in the sub-scanning direction, said powers being different from each other;
in that said refraction section has a plastic toric lens having a power in the main scanning direction and a power in the sub-scanning direction, said powers being different from each other; and so on.
A further color image forming apparatus of the present invention is a color image forming apparatus comprising plural sets of a scanning optical device and an image carrying member corresponding thereto, said scanning optical device having an imaging system comprising a refraction section having at least one refracting optical element and a diffraction section having at least one diffracting optical element, the color image forming apparatus being arranged to guide light emitted from each scanning optical device onto a surface of each corresponding image carrying member, to scan the surfaces of the image carrying members with the respective beams, to form images of different colors on the surfaces of the respective image carrying members, and to form a color image from the images formed on the surfaces of the plural image carrying members,
wherein each of the plurality of scanning optical devices is arranged in such a manner that an irradiation position of the light on the surface of the image carrying member is adjusted by displacing the diffracting optical element, and
wherein each of said plural scanning optical devices is arranged in such a manner that asymmetric magnification (component of slope of magnification) in the main scanning direction on the surface of the image carrying member is adjusted by displacing the refraction section or a scanning section comprising the refraction section and a deflecting element or/and the diffraction section in the main scanning direction.
Particularly, the color image forming apparatus is characterized:
in that said diffracting optical element is constructed as a separate unit from the other optical elements forming said scanning optical device;
in that a direction of displacement of the diffracting optical element is a direction of rotation about the optical axis or a direction of rotation about an axis along the longitudinal direction of the diffracting optical element and the diffracting optical element is arranged to be rotatable independently in each of these directions;
in that a slant of a scanning line on the surface of said image carrying member is adjusted by rotating said diffracting optical element about the optical axis or within a plane normal to the optical axis;
in that a curve of a scanning line on the surface of said image carrying member is adjusted by rotating said diffracting optical element about the axis along the longitudinal direction of the diffracting optical element;
in that said diffracting optical element is displaced based on a signal from detecting means for detecting registration;
in that said diffracting optical element has a power in the main scanning direction and a power in the sub-scanning direction, said powers being different from each other;
in that said refraction section has a plastic toric lens having a power in the main scanning direction and a power in the sub-scanning direction, said powers being different from each other;
in that each unit of said refraction section or the scanning section comprising the refraction section and the deflecting element and said diffraction section is fixed to a sheet metal stay;
in that a direction of displacement in the main scanning direction of said refraction section or the scanning section comprising the refraction section and the deflecting element and said diffraction section is a direction parallel to the main scanning direction or a direction of rotation about the optical axis within a plane including the main scanning direction; and so on.
Still another color image forming apparatus of the present invention is a color image forming apparatus comprising plural sets of a scanning optical device and an image carrying member corresponding thereto, said color image forming apparatus being arranged to guide light emitted from each scanning optical device onto a surface of each corresponding image carrying member, to scan the surfaces of the image carrying members with the respective beams, to form images of different colors on the surfaces of the respective image carrying members, and to form a color image from the images formed on the surfaces of the plural image carrying members,
each of said plural scanning optical devices comprising:
light source means comprising a semiconductor laser;
a first optical element for converting light emitted from the light source means into a substantially parallel beam;
a second optical element for focusing the substantially parallel beam thus converted, into a line image longitudinal in the main scanning direction on a deflection surface of a deflecting element; and
a third optical element comprising a refraction section having at least one refracting optical element and a diffraction section having at least one diffracting optical element for focusing a beam deflected by the deflecting element in a spot shape on the surface of the image carrying member,
wherein each of said plural scanning optical devices is arranged in such a manner that an irradiation position of the beam on the surface of the image carrying member is adjusted by displacing the diffracting optical element, and
wherein each of said plural scanning optical devices is arranged in such a manner that asymmetric magnification (component of slope of magnification) in the main scanning direction on the surface of the image carrying member is adjusted by displacing the refraction section or a scanning section comprising the refraction section and the deflecting element or/and the diffraction section in the main scanning direction.
Particularly, the color image forming apparatus is characterized:
in that said diffracting optical element is constructed as a separate unit from the other optical elements forming said scanning optical device;
in that a direction of displacement of the diffracting optical element is a direction of rotation about the optical axis or a direction of rotation about an axis along the longitudinal direction of the diffracting optical element and the diffracting optical element is arranged to be rotatable independently in each of these directions;
in that a slant of a scanning line on the surface of said image carrying member is adjusted by rotating said diffracting optical element about the optical axis or within a plane normal to the optical axis;
in that a curve of a scanning line on the surface of said image carrying member is adjusted by rotating said diffracting optical element about the axis along the longitudinal direction of the diffracting optical element;
in that said diffracting optical element is displaced based on a signal from detecting means for detecting registration;
in that said diffracting optical element has a power in the main scanning direction and a power in the sub-scanning direction, said powers being different from each other;
in that said refraction section has a plastic toric lens having a power in the main scanning direction and a power in the sub-scanning direction, said powers being different from each other;
in that each unit of said refraction section or the scanning section comprising the refraction section and the deflecting element and said diffraction section is fixed to a sheet metal stay;
in that a direction of displacement in the main scanning direction of said refraction section or the scanning section comprising the refraction section and the deflecting element and said diffraction section is a direction parallel to the main scanning direction or a direction of rotation about the optical axis within a plane including the main scanning direction; and so on.
A further scanning optical device of the present invention is a scanning optical device for scanning a surface to be scanned, using an imaging system comprising a refraction section having at least one refracting optical element and a diffraction section having at least one diffracting optical element,
said scanning optical device being arranged in such a manner that an irradiation position of a beam on the surface to be scanned is adjusted by displacing the diffracting optical element, and
said scanning optical device being arranged in such a manner that asymmetric magnification (component of slope of magnification) in the main scanning direction on the surface to be scanned is adjusted by displacing the refraction section or a scanning section comprising the refraction section and a deflecting element or/and the diffraction section in the main scanning direction.
Particularly, the scanning optical device is characterized:
in that said diffracting optical element is constructed as a separate unit from the other optical elements forming said scanning optical device;
in that a direction of displacement of the diffracting optical element is a direction of rotation about the optical axis or a direction of rotation about an axis along the longitudinal direction of the diffracting optical element and the diffracting optical element is arranged to be rotatable independently in each of these directions;
in that a slant of a scanning line on the surface to be scanned is adjusted by rotating said diffracting optical element about the optical axis or within a plane normal to the optical axis;
in that a curve of a scanning line on the surface to be scanned is adjusted by rotating said diffracting optical element about the axis along the longitudinal direction of the diffracting optical element;
in that said diffracting optical element has a power in the main scanning direction and a power in the sub-scanning direction, said powers being different from each other;
in that said refraction section has a plastic toric lens having a power in the main scanning direction and a power in the sub-scanning direction, said powers being different from each other;
in that each unit of said refraction section or the scanning section comprising the refraction section and the deflecting element and said diffraction section is fixed to a sheet metal stay;
in that a direction of displacement in the main scanning direction of said refraction section or the scanning section comprising the refraction section and the deflecting element and said diffraction section is a direction parallel to the main scanning direction or a direction of rotation about the optical axis within a plane including the main scanning direction; and so on.